It is true. Do a search for CO2 hydration.
While the proportion of carbonic acid is low, it is a time and temperature dependent reaction and we know that the quality of carbonation improves with time, even though we can get a bunch of carbon dioxide into solution in a very short time. I contend that it is the CO2 hydration that affects carbonation quality, not quantity.
yes I did check on carbonic acid formation and because of that I think it can't be used to explain the smoother carbonation.
at 25 C, 99.8 % of the CO2 is not converted to carbonic acid since equiblibrium will be reached before that. To me that's too little carbonic acid to make a difference. In addition to that, shouldn't soda, that sits on the shelf for a long time, also get a more softer carbonation?
Martin, I think what we have here is that the slow conversion of CO2 to carbonic acid seems a good fit to explain why beer carbonation becomes smoother with age. But that theory doesn't hold if the other aspects are considered as well.
I'm not saying that it can't play a role. I'm just contesting the mechanism and theory that have been proposed so far.